STRAM with composite free magnetic element

Abstract

Spin-transfer torque memory includes a composite free magnetic element, a reference magnetic element having a magnetization orientation that is pinned in a reference direction, and an electrically insulating and non-magnetic tunneling barrier layer separating the composite free magnetic element from the magnetic reference element. The free magnetic element includes a hard magnetic layer exchanged coupled to a soft magnetic layer. The composite free magnetic element has a magnetization orientation that can change direction due to spin-torque transfer when a write current passes through the spin-transfer torque memory unit.

What is claimed is: 
     
       1. A spin-transfer torque memory unit, comprising:
 a free magnetic element comprising a hard magnetic layer exchanged coupled to a soft magnetic layer, the hard magnetic layer has a saturation moment of less than 1000 emu/cm 3  and a coercively value that is equal to or greater than 1000 Oersteds, the free magnetic element having a magnetization orientation that can change direction due to spin-torque transfer when a write current passes through the spin-transfer torque memory unit; 
 a reference magnetic element having a magnetization orientation that is pinned in a reference direction; and 
 an electrically insulating and non-magnetic tunneling barrier layer separating the free magnetic element from the magnetic reference element. 
 
     
     
       2. A spin-transfer torque memory unit according to  claim 1 , wherein the soft magnetic layer has a spin polarization value greater than 0.5. 
     
     
       3. A spin-transfer torque memory unit according to  claim 1 , wherein the hard magnetic layer has uniaxial magnetic anisotropy. 
     
     
       4. A spin-transfer torque memory unit according to  claim 1 , wherein the free magnetic element has an aspect ratio of 1. 
     
     
       5. A spin-transfer torque memory unit according to  claim 1 , wherein the soft magnetic layer has a coercively value that is equal to or less than 500 Oersteds. 
     
     
       6. A spin-transfer torque memory unit according to  claim 1 , wherein the hard magnetic layer has a saturation moment of less than 500 emu/cm 3 . 
     
     
       7. A spin-transfer torque memory unit, comprising:
 a free magnetic element comprising a granular hard magnetic layer exchanged coupled to a soft magnetic layer, the soft magnetic layer having a coercivity value less than 500 Oersteds, the granular hard magnetic layer comprising a plurality of hard magnetic particles separated by non-magnetic material, the free magnetic element having a magnetization orientation that can change direction due to spin-torque transfer when a write current passes through the spin-transfer torque memory unit; 
 a reference magnetic element having a magnetization orientation that is pinned in a reference direction; and 
 an electrically insulating and non-magnetic tunneling barrier layer separating the free magnetic element from the magnetic reference element. 
 
     
     
       8. A spin-transfer torque memory unit according to  claim 7 , wherein the soft magnetic layer has a spin polarization value greater than 0.5. 
     
     
       9. A spin-transfer torque memory unit according to  claim 7 , wherein the hard magnetic particles have uniaxial magnetic anisotropy and a coercively value greater than 1000 Oersteds. 
     
     
       10. A spin-transfer torque memory unit according to  claim 7 , wherein the free magnetic element has an aspect ratio of 1. 
     
     
       11. A spin-transfer torque memory unit according to  claim 7 , wherein the hard magnetic particles have a saturation moment of less than 500 emu/cm 3 . 
     
     
       12. A spin-transfer torque memory unit according to  claim 7 , wherein the matrix of non-magnetic material is electrically insulating. 
     
     
       13. A spin-transfer torque memory unit according to  claim 12 , further comprising an electrically conducting layer in electrical contact with the hard magnetic particles and the hard magnetic particles being in electrical contact with the soft magnetic layer. 
     
     
       14. A spin-transfer torque memory unit, comprising:
 a free magnetic element comprising a hard magnetic layer exchanged coupled to a soft magnetic layer, the free magnetic element having a magnetization orientation that can change direction due to spin-torque transfer when a write current passes through the spin-transfer torque memory unit; 
 a reference magnetic element having a magnetization orientation that is pinned in a reference direction; 
 an electrically insulating and non-magnetic tunneling barrier layer separating the free magnetic element from the magnetic reference element; and 
 a magnetic compensation element adjacent to the free magnetic element, the magnetic compensation element applying a bias field on the magnetization orientation of the free magnetic element, wherein the bias field reduces a write current magnitude required to switch the direction of the magnetization orientation of the free magnetic element. 
 
     
     
       15. A spin-transfer torque memory unit according to  claim 14 , further comprising a non-magnetic spacer layer separating the magnetic compensation element from the free magnetic element. 
     
     
       16. A spin-transfer torque memory unit according to  claim 14 , wherein the soft magnetic layer has a spin polarization value greater than 0.5, and the hard magnetic layer has uniaxial magnetic anisotropy and a coercivity value greater than 1000 Oersteds. 
     
     
       17. A spin-transfer torque memory unit according to  claim 14 , wherein the hard magnetic layer comprising a plurality of hard magnetic particles in a matrix of non-magnetic material. 
     
     
       18. A spin-transfer torque memory unit according to  claim 17 , wherein the matrix of non\-magnetic material is electrically insulating.